Many large mobile machines such as mining trucks, locomotives, marine applications and the like have recently begun using alternative fuels, alone or in conjunction with traditional fuels, to power their engines. For example, large displacement engines may use a gaseous fuel, alone or in combination with a traditional fuel such as diesel, to operate. Because of their relatively low densities, gaseous fuels, for example, natural gas or petroleum gas, are carried onboard vehicles in liquid form. These liquids, the most common including liquefied natural gas (LNG) or liquefied petroleum gas (LPG), can be cryogenically stored in insulated tanks on the vehicles, or may alternatively be stored at an elevated pressure, for example, a pressure between 30 and 300 psi in a pressurized vessel. In either case, the stored fuel can be pumped, evaporated, expanded, or otherwise placed in a gaseous form in metered amounts and provided to fuel the engine.
To store and utilize cooled natural gas in compressed or liquefied forms onboard mobile machines, specialized storage tanks and fuel delivery systems may be required. This equipment may include a double-walled cryogenic tank and a pump for delivering the LNG or LPG to the internal combustion engine for combustion. The pumps that are typically used to deliver the LNG to the engine of the machine include pistons, which deliver the LNG to the engine. Such piston pumps, which are sometimes also referred to as cryogenic pumps, will often include a single piston that is reciprocally mounted in a cylinder bore. The piston is moved back and forth in the cylinder to draw in and then compress the gas. Power to move the piston may be provided by different means, the most common being electrical, mechanical or hydraulic power.
One example of a cryogenic pump can be found in U.S. Pat. No. 3,212,280 (the '280 patent), which describes a pumping system for volatile liquids that includes three individual pumping units that are contained within a bell-shaped housing. The individual pumps each include a single piston that may be driven by a mechanical slider crank drive mechanism. The drive mechanism is disposed outside of the tank.